1. Field of the Invention
The present invention relates to an image forming apparatus such as a copy machine and a printer.
2. Description of the Related Art
Conventional image forming apparatuses using a two-component developer include one which uses a toner bottle for replenishing the apparatus with toner in order to maintain charging characteristics of toner. When there becomes no toner in a toner bottle, the toner bottle is replaced with a new toner bottle. As described in Japanese Patent Laid Open No. 2005-62848, absence of toner (no toner) is decided responsively to a value of a toner density sensor which measures TD ratio of the two-component developer stored in the developing container. After a toner bottle is changed, a toner density recovery sequence for recovering toner density is performed. In the toner density recovery sequence, whether the toner bottle is changed with a new bottle or not is decided responsively to a value of the toner density sensor.
A problem of the toner density recovery sequence is that the image forming apparatus cannot be used right after a toner bottle is changed. For a user who exchanges a toner bottle, it could be stressful not to be able to use the image forming apparatus right after exchange of a toner bottle. Therefore, it is desired in view of usability that the image forming apparatus can be used right after exchange of a toner bottle.
However, when image forming is allowed without performing the toner density recovery sequence, toner supply is performed with the TD ratio lowered. Therefore, when the same supply sequence as usual is performed, the TD ratio suddenly increases because supply quantity is large, causing the charging characteristics of toner to change a lot. In this case, in the image forming immediately after the exchange, a density change per a sheet becomes large. Thereby the user is liable to recognize the color change. Further, when the TD ratio rapidly increases, an overshoot may occur, in which the TD ratio exceeds the target value. In order to lower the TD ratio, it is necessary to wait for consumption of toner by image forming and the TD ratio exceeds the target value for a certain time period.
Therefore, Japanese Patent Laid Open No. 2008-209795 discloses the structure in which a target value of toner supply control is lowered as compared with the usual image forming immediately after the image forming is allowed, thereby limiting supply amount. However, in the above configuration, a rapid rise in the TD ratio is suppressed, but it is done by changing the initial TD ratio after exchange, so there is a possibility that the TD ratio deviates significantly from the desired TD ratio.